Television image tube



P. SCHAGENK TELEVISION IMAGE TUBE Dec 16, 1952 Filed July 7, 1950 njw iii

CONDUCT/V5 MATERIAL {5-4004 jNVENTOR.

PIETER SCH fi- %GEN AGENT Patented Dec. 16, 1952 UNITED STATES PATENT OFFICE.

TELEVISION IMAGE TUBE Application July 7, 1950, Serial No. 172,439 In the Netherlands July 9, 1949 9 Claims.

This invention relates to television transmitting tubes and more particularly to the image analyzing screens of such devices in which a directive electron beam is employed for screen scanning.

It is an important object of the invention to provide a television transmitting tube having a novel form of image analyzing screen.

Still another object of the invention is to provide a television transmitting tube having an image analyzing screen which is simple and relatively inexpensive to manufacture.

According to the invention the above objectives are achieved, if in a television transmitting tube having a source of a directive electron beam, the image analyzing screen comprises a substance,

the dielectric constant of which varies with variations in the intensity of the light projected onto the screen. This light sensitive substance in the device of invention is applied to an electrically conductive surface of a carrier, and the opposite side of this substance is coated with a thin layer of insulating material. The directive electron beam of the tube scansthis thin layer of insulating material occasioning a varying potential differential across the light sensitive substance cor responding to the variations in the light intensity of the image formed on the screen. These potential variations are then converted to successive current variations which may be amplified in the well-known manner for transmission.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows diagrammatically a television transmitting tube in which the invention is used.

Fig. 2 is a fragmentary sectional view of the television transmitting tube of Fig. l.

Referring to Fig. 1 the electrode system I produces a directive electron beam 2. The system i and the image collecting or analyzing screen 3 are housed in an exhausted glass vessel 4. The electrode system I is of a usual type and comprises an electron-emitting cathode 5, a Wehnelt electrode 6, a first anode l and a final anode 8. Use may be made of electro-static fields or of magnetic fields for focusing the beam 2 on the screen 3. For supplying the required voltages to the electrodes of the electrode system use may be made of a voltage source 9, the positive terminal of which is furthermore connected to a collecting electrode It, which may preferably be in the form of a conductive coating on the tube wall 4,. .Such a coating may be a graphite deposit for example. In the particular embodiment shown, this electrode I9 is connected through a resistance H to the screen 3. .By means of the optical lens I2 the image of an ob ject I3 to be transmitted by the device is projected onto the image analyzing screen 3. The electron beam is deflected in directions at right angles to each other by means of the magnetic fields. As the deflection members required for this purpose, a couple of coils it are shown by which the beam is deflected at right angles to the plane of the drawing.

The projection screen 3 as shown more clearly in Fig. 2 consists of a transparent support [5 of insulating material, for example, of mica, to

which is applied a thin transparent layer It of electrically conductive material. This layer It may consist of chromium, iridium or platinum and is termed the signal plate. It constitutes the common coating of the image analyzer system operating as a multiple capacitor. The dielectric ll consists of a substance which is sensitive to actinic rays and of which the dielectric constant varies with the irradiation intensity. Known substances having this property are, for example zinc sulphide, cadmium sulphide, zinc selenide, cadmium selenide or a mixture of two or more of these substances. In the manufacture and working up of these materials methods already known in connection with sulphides and selenides may be utilised. Thus for increasing sensitivity, fluxes may be added, preferably fluxes which do not increase the conductivity of the substance, e. g. magnesium fluoride as already known the spectral sensitivity can be increased by a copper or silver addition. This dielectric is coated with an insulating layer It. If this layer is is transparent, the image may be projected either onto one or onto the other side of the screen 3. The insulating layer should then be as thin as possible, in order that a maximum portion of the image producing rays may pass. However, the electrons of the beam are just prevented from passing. A layer thickness of approximately 0.2 is advantageous in this respect. This layer l3 may be, for instance, of silicon dioxide or other suitable material and the layer may be obtained by applying these substances by vaporisation.

The counter-coating co-eperating with the signal plate It in the multipie capacitor system which forms the image-electrode is constituted by the point of impact of the electron beam 2 on the insulating layer H3. This point of impact has finite dimensions and, since the beam moves i1ccessantly, the point of impact sweeps across the surface of layer l8. For purposes of illustration it may be assumed that the beam spot stays for an instant at the point indicated in Figure 2. By means of the voltage source 9 the electron velocity may be adjusted in a manner such that the number of secondary electrons released at the point of impact of the beam on the layer I8 exceeds the number of primary electrons in the beam striking the screen. Consequently, the secondary-emission coefiicient exceeds unity. Initially, substantially the whole secondary-emission current is carried oif to the collecting electrode Ill, so that the potential of the surface area on the layer I3 struck by the beam increases. This potential increase which amounts to a few volts, produces a counter-field relative to the collecting electrode it, so that gradually fewer electrons are carried off to the latter. Apart from the electrons wandering to the collecting electrode, part of the secondary-emission electrons spreads over the surface of the insulating layer [8. These electrons cause the potential of this surface todecrease to a value slightly lower than the potential of the collecting electrode. In this manner a potential jump which, at a constant electron velocity is uniform for any point of the surface, occurs at the surface struck by the beam relative to the remaining part thereof. Consequently, the variation of the electric charge of each capacitor element thus produced depends upon the capacity of the image element i. e. upon the dielectric constant of the beam-sensitive substance at this area. The latter varies with the intensity of exposure and increases as the intensity of the light of exposure increases, with the result that the electric charge also increases. Consequently, an electric current is produced across the connection between the signal electrode l6 and the collecting electrode Hi, the variations of which current correspond with the charge variations and consequently with the dielectric constant variation. This current produces across the resistance I l a voltage which is supplied to the grid of the amplifying tube Hi.

It is evident that with a beam swinging continuously across a continuous surface, the supply of the electric charge by the beam and its levelling by electron-spread over the surface with varying exposure, show themselves in the mean value of the signal current through the resistance,

What I claim is:

1. A television tube for the transmission of images comprising an envelope, a source of a directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in'the path of said directive electron beam, said screen comprising a body portion of a substance having a variable dielectric constant responsive to light intensity variations, an insulating coating portion on the side of said body portion facing said electron beam source, and a support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

2. A television tube for the transmission of images comprising an envelope having a light transparent portion, a source of a directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam and exposed to light from said transparent portion, said. screen GQIflprising a body portion of a substance having a variable dielectric constant responsive to light intensity variations, an insulating coating portion on the side of said body portion facing said electron beam source, and a support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

3. A television tube for the transmission of images comprising a glass envelope, a source of a directive beam of electrons within said envelope, a conductive coating collecting electrode on said envelope wall and spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of a substance having a variable dielectric constant responsive to light intensity variations, a thin insulating coating portion on the side of said body portion facing said electron beam source, and a light transparent portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

4. A television tube for the transmission of images comprising a glass envelope, a source of directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of a mixture of substances each of said substances having variable dielectric constant responsive to light intensity variations, an insulating coating portion on the side of said body portion facing said electron beam source, and a support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surfacecontacting said body portion.

5. A television tube for the transmission of images comprising a glass envelope, a source of a directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of zinc sulphide having a variable dielectric constant responsive to light intensity variations, 2, thin insulating coating of silicon dioxide on the side of said body portion facing said electron beam source, and a light transparent portion on the side of said body portion remote from said electron beam source and'having an electrically conductive surface contacting said body portion.

6. A television tube for the transmission of images comprising a glass envelope, a source of a directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of cadmium sulphide having a variable dielectric constant responsive to light intensity variations, a thin insulating coating of silicon dioxide on the side of said body portion facing said electron beam source, and a support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

7. A television tube for the transmission of images comprising a glass envelope, a source of a directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of zinc selenide having a variable dielectric constant responsive to light intensity variations, a thin insulating coating of silicon dioxide on the side of said body portion facing said electron beam source, and a, light transparent support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

8. A television tube for the transmission of images comprising a glass envelope, a source of a. directive beam of electrons within said envelope, a collecting electrode spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a body portion of cadmium selenide having a variable dielectric constant responsive to light intensity variations, a thin insulating coating of silicon dioxide on the side of said body portion facing said electron beam source, and a light transparent portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

9. A television tube for the transmission of images comprising a glass envelope, at source of 6 directive beam of electrons within said envelope, a conductive coating collecting electrode on said tube envelope surrounding the path of said directive beam and spaced from said beam source, and an image screen within said envelope and spaced from said collector electrode and in the path of said directive electron beam, said screen comprising a, body portion of a mixture of zinc sulphide and cadmium sulphide having a variable dielectrict constant responsive to light intensity variations, a thin insulating coating of silicon dioxide on the side of said body portion facing said electron beam source, and a light transparent support portion on the side of said body portion remote from said electron beam source and having an electrically conductive surface contacting said body portion.

PIETER SCI-IAGEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,013,162 McC'reary Sept. 3, 1935 2,541,374 Morton Feb. 13, 1951 FOREIGN PATENTS Number Country Date 271.401 Great Britain June 16. 1927 

